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The Trouble with Time Travel

April 11, 2013

While I'm glad to see the return of Rachel and Leigh and to meet our new adventurer Hunter, they need to be extremely careful while traipsing around in the past. Why? If time travel is possible, it could be very dangerous. This is not just because one could get eaten by a T. Rex or burned at the stake. One's own existence and possibly the very fabric of reality itself could be at stake.

It all boils down to causality. Causality is exactly what it sounds like, the relationship of cause and effect. The history of the universe is a very long chain of cause and effect, and altering that chain could lead to serious problems known as paradoxes. Let’s take a look at two paradoxes that arise in the context of the Terminator franchise.

The first is called the grandfather paradox: you travel back in time and alter history so that your parents never meet (the classic case is that you kill your grandfather while he was still a child.) It, therefore, follows that you were never born. So how is it that you were able to travel to the past and kill your grandfather if you were never born? The problem becomes even greater as you go further into the past, leading to the butterfly effect. A seemingly insignificant change in the deep past (such as killing a single butterfly) could ripple out through history and radically alter the course of subsequent events.

The second paradox is the ontological paradox, where an effect is its own cause. Suppose you win the lottery because an elderly man or woman bought you a ticket with the winning number. You use the hundreds of millions of dollars to research and develop a time machine. After a lifetime of work, you use the time machine to go back in time and buy your younger self the winning ticket because you know the winning number. It should be clear that the relationship of cause and effect has gone seriously awry here.

Here are some of the paradoxes involved in just the first two films of the Terminator franchise. The situation gets even more convoluted when one considers T3 and The Sarah Connor Chronicles, so we’ll disregard them for now.

Ontological Paradox #1. Skynet sends a Terminator back in time to kill Sarah Connor. In order to protect his mother Sarah and thus his own existence, John Connor sends Kyle Reese back to the same time as the Terminator. Reese falls in love with Sarah and fathers John. Thus, John is responsible for his own birth.

Ontological Paradox #2. Skynet uses its advanced technology to build Terminators. The technology used to create Skynet is derived from the remains of the first Terminator sent back in time to kill Sarah Connor. Thus, Skynet is essentially its own parent.

Ontological Paradox #3. John Connor leads the human resistance to victory over Skynet, but he never would have existed had Skynet not sent the first Terminator back in time, which required Connor to send Kyle Reese back in time to protect Sarah, where he fathers John.Thus, Skynet is responsible for its own defeat. In fact, this led Skynet to the last ditch effort to send Terminators back in time to eliminate Sarah and John Connor, which sets the whole chain of events off in the first place.

Grandfather Paradox #1. By sending the T-1000 back to kill John Connor in T2, Skynet sets off a chain of events whereby Sarah Connor learns that Skynet is derived from the wreckage of the first Terminator. Sarah is successful in destroying the computer lab where Skynet technology is being developed and destroys the remains of the first Terminator. Thus, Skynet cannot have existed in the first place.

Grandfather Paradox #2. By destroying the remains of the first Terminator (and the second Terminator sent to protect Sarah and John), the technology necessary to create Skynet in the first place no longer exists. If Skynet were never created, there would be no need for Kyle Reese to travel into the past to protect Sarah Connor, so he would never fall in love with her and father John Connor. Thus, John Connor never could have existed in the first place.

In essence, John Connor and Skynet are trapped in a tangle of timelines awash in paradoxes with no way out. Are you feeling a bit confused? A little explanation on the nature of time might be in order here.

The Doctor’s highly technical explanation aside, how can we maintain causality and avoid paradoxes in a universe where time travel is possible? The first possibility is the most likely: although time travel has indeed been found to be possible under certain theoretical conditions, such conditions cannot be met in the real world. After all, if time travel becomes possible at some point in the future, why aren’t we overrun with time travelling tourists from the future?

But if time travel is possible, perhaps the solution is the creation of multiple timelines: in the case of the grandfather paradox, there is one timeline in which you were born, and one that you created by preventing your parents from meeting. Another possibility is that you might be able to travel into the past, but events would conspire to prevent you from altering the overall course of history or threatening your own existence. T3 and the Sarah Connor Chronicles invoke these principles in the Terminator franchise, resolving some of the paradoxes but leading to yet further complications.

The Terminator franchise is not the only fictional world where time travel paradoxes run rampant. If you haven’t had enough of the wibbly-wobbly timey-wimey conundrums in just this one franchise, here are some other fictional worlds where time travel paradoxes play a major role: